This invention relates to an fuel injector for use in supplying fuel, under pressure, to the cylinders of an internal combustion engine.
A known fuel injector arrangement comprises a plunger reciprocable within a bore provided in a housing to pressurize fuel located within a pump chamber defined by the bore. The pump chamber communicates with a fuel pressure actuated injector such that once the fuel pressure within the pump chamber exceeds a predetermined level, the injector opens and, thus, fuel injection commences.
In order to permit independent control of the injection pressure and the timing of injection, it is known to provide a spill valve which communicates with the pump chamber, and an injection control valve which controls the pressure applied to a control chamber defined, in part, by a surface associated with a needle of the injector to control movement of the needle. In use, the spill valve remains open during initial inward movement of the plunger. Subsequently, the spill valve is closed, further inward movement of the plunger pressurizing the fuel within the pump chamber. When injection is to commence, the injection control valve is actuated to connect the control chamber to a low pressure drain thus permitting movement of the needle away from its seating to commence fuel injection.
It has also been proposed to arrange the injection control valve such that it is biased into a position in which the control chamber communicates with the low pressure drain. Actuation of the injection control valve causes communication between the low pressure drain and the control chamber to be broken and permits fuel under high pressure to flow into the control chamber.
Conventionally, movement of the spill valve and the injection control valve is controlled by means of two separate actuators. Each actuator comprises a winding and two poles, each winding requiring separate and independent electrical connections. The electrical connections to the actuators can be difficult to accommodate within the fuel injector housing. Furthermore, the twin-poles of each actuator occupy a relatively large space. This has disadvantages in terms of size and cost.
It is an object of the present invention to provide a fuel injector which alleviates these disadvantages.
According to the present invention there is provided a fuel injector for use in an injector arrangement including a fuel pump having a pump chamber and a spill valve arrangement including a spill valve member which is engageable with a spill valve seating to control communication between the pump chamber and a low pressure drain, a valve needle which is engageable with a valve needle seating, a control chamber arranged such that the fuel pressure therein urges the valve needle towards its seating, a control valve arrangement, including a control valve member, for controlling the fuel pressure within the control chamber, and an actuator arrangement for controlling movement of the spill valve member and the control valve member, the actuator arrangement comprising a double pole actuator having a first armature which is movable with the spill valve member and a single pole actuator having a second armature which is movable with the control valve member.
The invention provides the advantage that a reduced space is required to accommodate the actuator arrangement as one of the actuators is of the single pole type.
Conveniently, the spill valve member is of relatively large diameter and the control valve member is of smaller diameter. The control valve member may be engageable with first and second control valve seatings to control communication between the pump chamber and the control chamber and between the control chamber and the low pressure drain.
Conveniently, the control valve member may be provided with resilient bias means for biasing the control valve member against the second control valve seating to close communication between the control chamber and the low pressure drain. Conveniently, the spill valve member may be provided with further resilient bias means for biasing the spill valve member away from the spill valve seating to open communication between the pump chamber and the low pressure drain.
The first and further resilient bias means may take the form of first and second compression springs. Alternatively, the first and further resilient bias means may be provided by a single compression spring.
Although the single pole actuator only provides a relatively weak force, as the control valve member is only of relatively small diameter the force provided by the single pole actuator is sufficient to move the control valve member away from the second control valve seating against the first control valve seating. The double pole actuator provides a larger force which permits a spill valve member of relatively large diameter to be employed. As the spill valve member can have a relatively large diameter, a relatively high rate of flow of fuel is permitted past the spill valve seating when the spill valve is open.
The actuator arrangement is conveniently housed within an actuator housing. The actuator housing may be provided with a drilling which forms part of a supply passage for fuel which communicates with the pump chamber. It is possible for the supply passage to be formed, in part, within the actuator housing as the actuator arrangement occupies a reduced space within the actuator housing.
Conveniently, the actuator arrangement comprises first and second windings associated with first and second actuators respectively. The first and second windings may be arranged such that they share a common electrical connection. Thus, fewer electrical connections to the fuel injector are required.
According to another aspect of the present invention, there is provided an actuator arrangement for use in an injector arrangement including a fuel pump having a pump chamber, a spill valve arrangement including a spill valve member which is engageable with a spill valve seating to control communication between the pump chamber and a low pressure drain and a control valve arrangement, including a control valve member, for controlling the fuel pressure within a control chamber, the actuator arrangement comprising a double pole actuator having a first armature which is movable with the spill valve member and a single pole actuator having a second armature which is movable with the control valve member.